The population of oomycete Plasmopara halstedii (Farl.) Berl. et de Toni (sunflower downy mildew pathogen) has been monitored in Krasnodar and Rostov regions and the Republic of Adygea for more than 15 years. Prior to the beginning of the 2000s there were races 100, 300, 310 and 330 in the regions. In the period from 2004 to 2007 races 100, 300, 310 and 700 were recorded sporadically. The race 330 was the most common; in a number of agrocoenoses it was 100 % of samples. In some fields races 710 and 730 prevailed. In 2008–2011 only races 330, 710 and 730 were found; the race 330 have been still prevailed and was also found on Ambrosia artemisiifolia L. Since 2012, in the majority of fields races 710 and 730 prevailed, and the race 330 wasn’t allocated in many of them; for the first time in Russia pathotype 334, that able to overcome Pl6, was found in Krasnodar region. In the period of 2013–2015 increased distribution of the race 334 in the Krasnodar region and the Republic of Adygea was observed. At the same time, in 2014 in one field in the Rostov region only races 310 and 330 (prevailed) were identified. The virulence of the pathogen population is closely connected with the cultivated assortment of sunflower. Further spread and accumulation of P. halstedii race 334 and the emergence of new pathogen pathotypes in the said regions are predicted.

Fusarium fungi have grown from a minor pathogen of sunflower crop to a major problem of sunflowers in Russia. The aim of this work was breeding for resistance to this new major pathogen, combining field and laboratory testing in the framework of VNIIMK hybrid sunflower breeding program. Four segregated hybrid combinations selected on the basis of their field resistance to different pathogens were used as breeding material. Three of them were doublecross combinations: F 3 R-14 × (VK-591 × VK-539), F 4 VK-623 × (HA-385 × VK-653) and F 4 (VK-678 A × VK-464) × VK-541, the fourth one was a cross F 3 VK-680 × O.P. variety Leader. It was shown that combination of laboratory testing and individual selection can rapidly improve the Fusarium resistance of a segregated population -the share of families without plants with Fusarium damage symptoms was 62.5% among the selected plants offspring while only 18.2% of such families were found in the breeding nursery the next year after selection. As a result, a number of new breeding lines were developed that exhibited no Fusarium symptoms in the field.

The samples of Plasmopara halstedii (the causal agent of sunflower downy mildew) were collected on sunflower fields in south of the Russian Federation: in the Krasnodar, Rostov and Stavropol regions, and in the Republic of Adygea in 2016 and 2017. Virulence code of 545 isolates was identified; i. e. 280 isolates originating from 24 fields in 2016, and 265 isolates from 17 fields in 2017. Races 330, 334, 710 and 730, widespread within the region in previous years, were found in all mentioned areas. In addition, races 713, 733 and 734 have been detected in several districts of the Krasnodar region since 2016. This is the first report of these races in Russia and above that the first record throughout Europe and Asia for the races 733 and 734. The identification of new P. halstedii races was confirmed by the method of cross inoculations from individual differential lines. The phenotype corresponding to virulence code 734 was in some cases disclosed as a mixture of race 334 with 710 or 730. The presence of several P. halstedii races on an individual plant was also confirmed for the first time in the territory of the Russian Federation.

Sunflower downy mildew caused by Plasmopara halstedii (Farl.) Berl. et de Toni is a destructive and widespread disease. More than 50 races of P. halstedii have been recorded worldwide. In 2020, in the Russian Federation (Zernogradsky district, Rostov region), a globally new race 337 was identified for the first time. The pathogen was identified on the plants of a foreign sunflower hybrid bearing the resistance gene Pl₆. According to the five-digit racial nomenclature, its virulence profile was determined as 337 53. It is the first P. halstedii race recorded in the Russian Federation that simultaneously infects all differential lines of the 3^rd triplet, i.e., HA-R4, HA-R5 and HA-335. The sunflower lines RHA-274, 803-1, PSC8, RHA-419 and RHA-340 were resistant to it. All the collected isolates of the new race were susceptible to the fungicide mefenoxam.

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